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<h1>

  React v0.13 RC

</h1>

<p class="meta">
  February 24, 2015
  by
  
    
      <a href="https://twitter.com/zpao">Paul O’Shannessy</a>
    
    
  
</p>

<hr>

<div class="post">
  <p>Over the weekend we pushed out our first (and hopefully only) release candidate for React v0.13!</p>

<p>We&#39;ve talked a little bit about the changes that are coming. The splashiest of these changes is support for ES6 Classes. You can read more about this in <a href="/react/blog/2015/01/27/react-v0.13.0-beta-1.html">our beta announcement</a>. We&#39;re really excited about this! Sebastian also posted earlier this morning about <a href="/react/blog/2015/02/24/streamlining-react-elements.html">some of the other changes coming focused around ReactElement</a>. The changes we&#39;ve been working on there will hopefully enable lots of improvements to performance and developer experience.</p>

<p>The release candidate is available for download:</p>

<ul>
<li><strong>React</strong><br>
Dev build with warnings: <a href="https://fb.me/react-0.13.0-rc1.js">https://fb.me/react-0.13.0-rc1.js</a><br>
Minified build for production: <a href="https://fb.me/react-0.13.0-rc1.min.js">https://fb.me/react-0.13.0-rc1.min.js</a><br></li>
<li><strong>React with Add-Ons</strong><br>
Dev build with warnings: <a href="https://fb.me/react-with-addons-0.13.0-rc1.js">https://fb.me/react-with-addons-0.13.0-rc1.js</a><br>
Minified build for production: <a href="https://fb.me/react-with-addons-0.13.0-rc1.min.js">https://fb.me/react-with-addons-0.13.0-rc1.min.js</a><br></li>
<li><strong>In-Browser JSX transformer</strong><br>
<a href="https://fb.me/JSXTransformer-0.13.0-rc1.js">https://fb.me/JSXTransformer-0.13.0-rc1.js</a></li>
</ul>

<p>We&#39;ve also published version <code>0.13.0-rc1</code> of the <code>react</code> and <code>react-tools</code> packages on npm and the <code>react</code> package on bower.</p>

<hr>

<h2>Changelog</h2>

<h3>React Core</h3>

<h4>Breaking Changes</h4>

<ul>
<li>Mutating <code>props</code> after an element is created is deprecated and will cause warnings in development mode; future versions of React will incorporate performance optimizations assuming that props aren&#39;t mutated</li>
<li>Static methods (defined in <code>statics</code>) are no longer autobound to the component class</li>
<li><code>ref</code> resolution order has changed slightly such that a ref to a component is available immediately after its <code>componentDidMount</code> method is called; this change should be observable only if your component calls a parent component&#39;s callback within your <code>componentDidMount</code>, which is an anti-pattern and should be avoided regardless</li>
<li>Calls to <code>setState</code> in life-cycle methods are now always batched and therefore asynchronous. Previously the first call on the first mount was synchronous.</li>
<li><code>setState</code> and <code>forceUpdate</code> on an unmounted component now warns instead of throwing. That avoids a possible race condition with Promises.</li>
<li>Access to most internal properties has been completely removed, including <code>this._pendingState</code> and <code>this._rootNodeID</code>.</li>
</ul>

<h4>New Features</h4>

<ul>
<li>Support for using ES6 classes to build React components; see the <a href="/react/blog/2015/01/27/react-v0.13.0-beta-1.html">v0.13.0 beta 1 notes</a> for details</li>
<li>Added new top-level API <code>React.findDOMNode(component)</code>, which should be used in place of <code>component.getDOMNode()</code>. The base class for ES6-based components will not have <code>getDOMNode</code>. This change will enable some more patterns moving forward.</li>
<li>New <code>ref</code> style, allowing a callback to be used in place of a name: <code>&lt;Photo ref={(c) =&gt; this._photo = c} /&gt;</code> allows you to reference the component with <code>this._photo</code> (as opposed to <code>ref=&quot;photo&quot;</code> which gives <code>this.refs.photo</code>)</li>
<li><code>this.setState()</code> can now take a function as the first argument for transactional state updates, such as <code>this.setState((state, props) =&gt; ({count: state.count + 1}));</code> -- this means that you no longer need to use <code>this._pendingState</code>, which is now gone.</li>
<li>Support for iterators and immutable-js sequences as children</li>
</ul>

<h4>Deprecations</h4>

<ul>
<li><code>ComponentClass.type</code> is deprecated. Just use <code>ComponentClass</code> (usually as <code>element.type === ComponentClass</code>)</li>
<li>Some methods that are available on <code>createClass</code>-based components are removed or deprecated from ES6 classes (for example, <code>getDOMNode</code>, <code>setProps</code>, <code>replaceState</code>).</li>
</ul>

<h3>React with Add-Ons</h3>

<h4>Deprecations</h4>

<ul>
<li><code>React.addons.classSet</code> is now deprecated. This functionality can be replaced with several freely available modules. <a href="https://www.npmjs.com/package/classnames">classnames</a> is one such module.</li>
</ul>

<h3>React Tools</h3>

<h4>Breaking Changes</h4>

<ul>
<li>When transforming ES6 syntax, <code>class</code> methods are no longer enumerable by default, which requires <code>Object.defineProperty</code>; if you support browsers such as IE8, you can pass <code>--target es3</code> to mirror the old behavior</li>
</ul>

<h4>New Features</h4>

<ul>
<li><code>--target</code> option is available on the jsx command, allowing users to specify and ECMAScript version to target.

<ul>
<li><code>es5</code> is the default.</li>
<li><code>es3</code> restored the previous default behavior. An additional transform is added here to ensure the use of reserved words as properties is safe (eg <code>this.static</code> will become <code>this[&#39;static&#39;]</code> for IE8 compatibility).</li>
</ul></li>
<li>The transform for the call spread operator has also been enabled.</li>
</ul>

<h3>JSX</h3>

<h4>Breaking Changes</h4>

<ul>
<li>A change was made to how some JSX was parsed, specifically around the use of <code>&gt;</code> or <code>}</code> when inside an element. Previously it would be treated as a string but now it will be treated as a parse error. We will be releasing a standalone executable to find and fix potential issues in your JSX code.</li>
</ul>

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